Chapter 52 / Learning and Memory 1297
Figure 52–5 Long-term memory
is commonly classified as either
explicit (the memory is reported
verbally) or implicit (the memory is
expressed through behavior without
conscious awareness).
事实
(语义)
事件
(情节)
启动
程序性记忆
(技能和习惯)
联想学习: 经典条件
反射和操作条件反射
非联想学习:
习惯化和敏感性
两种形式的
长期记忆
内隐
(非陈述性)
外显
(陈述性)
nature and extent of their interactions are a topic of
ongoing investigation.
There are also ongoing debates about the role of
conscious awareness in memory and about whether it
is indeed a necessary feature of memories supported
by the medial temporal lobe. These debates are driven
by a growing body of work showing that the same
medial temporal circuits necessary for explicit memory
are also necessary for some forms of implicit memory
(as described below). Indeed, although episodic mem-
ory is typically assessed by asking subjects to report
the content of their memory, it remains unknown
whether conscious accessibility is an integral feature
of the memories themselves. Nonetheless, the distinc-
tion between implicit and explicit memory played an
important historical role in differentiating forms of
memory and still offers a productive framework for
considering the neural bases of memory. Thus, we use
the terms “explicit memory” and “implicit memory”
here to distinguish these two forms of memory and
the classes of subjective experience and behaviors that
they are based on. In the following sections, we focus
on episodic memory, which has been the target of a
great deal of cognitive neuroscience research in both
amnesic patients and healthy individuals.
Episodic Memory Processing Involves Encoding,
Storage, Retrieval, and Consolidation
Episodic memory has been studied extensively and
offers a window into understanding how the brain
builds, stores, and retrieves details about episodes in
our lives. We now know that the brain does not have
a single long-term store of episodic memories. Instead,
the storage of any item of knowledge is widely dis-
tributed among many brain regions that process dif-
ferent aspects of the content of the memory and can
be accessed independently (by visual, verbal, or other
sensory clues). Second, episodic memory is mediated
by at least four related but distinct types of processing:
encoding, storage, consolidation, and retrieval.
Encoding is the process by which new information
is initially acquired and processed during the formation
of a new memory. The extent of this processing is criti-
cally important for determining how well the learned
material will be remembered. For a memory to persist
and be well remembered, the incoming information
must undergo what the psychologists Fergus Craik and
Robert Lockhart called “deep” encoding. This is accom-
plished by attending to the information and associating
it with memories that were already established. Mem-
ory encoding is also stronger when one is motivated to
remember, whether because the information has par-
ticular emotional or behavioral relevance (eg, a memory
for a particularly delicious meal on an enjoyable first
date) or whether the information itself is neutral but is
associated with something meaningful (eg, remember-
ing the location of that restaurant).
Storage refers to the neural mechanisms and sites
by which the newly acquired information is retained
as a lasting memory over time. One of the remarkable
features about long-term storage is that it seems to
have an almost unlimited capacity. In contrast, work-
ing memory storage is very limited; psychologists
believe that human working memory can hold only a
few pieces of information at any one time.
Consolidation is the process that transforms tem-
porarily stored and still labile information into a more
stable form. As we shall learn in the next two chapters,
consolidation involves expression of genes and protein
synthesis that give rise to structural changes at synapses.
Finally, retrieval is the process by which stored
information is recalled. It involves bringing back to
mind different kinds of information that are stored
in different sites. Retrieval of memory is much like
perception; it is a constructive process and therefore
subject to distortion much as perception is subject to
illusions (Box 52–1). When a memory is retrieved, it
becomes active again, providing an opportunity for
an old memory to be encoded again. Because retrieval
is constructive, re-encoding of a retrieved memory
can differ from the original memory. For example,
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